1. Field of the Invention
This invention relates to a jet velocity measuring apparatus for measuring the velocity of a fluid stream. More particularly, this invention relates to a jet velocity measuring apparatus having a debris-deflecting slot for directing a curtain of air past the respective terminations of light-transmitting fiberoptic bundles of the measuring apparatus.
2. Information Disclosure Statement
U.S. Ser. No. 573,387 by Daniel Parker filed Jan. 24, 1984 and assigned to the Beloit Corporation teaches a method and apparatus for measuring the jet velocity adjacent a headbox of a papermaking machine. All the disclosure of the aforementioned pending patent application is incorporated by reference into the present application.
Copending U.S. Ser. No. 573,387 describes a first and a second fiberoptic bundle for measuring the flow velocity of pulp issuing from a headbox. More specifically, a first light beam passes through the first fiberoptic bundle towards the jet and is reflected back along the first fiberoptic bundle which is bifurcated thereby permitting the reflected beam to be transmitted to a first photosensitive device. The first photosensitive device generates a first electronic series of signals which correspond with that portion of the surface of the stream on which the first beam is reflected. A second beam of light passes through the second fiberoptic bundle towards the jet so that the second beam of light is reflected from the same portion of the stream downstream. The second beam of light is reflected back along the second fiberoptic bundle which is bifurcated enabling the second beam of light to be transmitted to a second photosensitive device to generate a second series of electronic signals. Various electronic apparatus is utilized to compare the first and second series of signals and to measure the time difference between a particular pattern of signals received from the second photosensitive device that correspond with signals received from the first photosensitive device indicating that that portion of the jet has flowed downstream towards the second beam of light. From the measurement of the time taken by such portion of the jet to flow between the first and second beam and knowing the distance between the beams of light, an accurate measure of the jet velocity is determinable.
Prior to the aforementioned copending application, various flow measuring devices had been proposed but most of the prior proposals involved the immersion of a pressure-sensitive device within the jet stream. Such pressure-sensitive devices, of necessity interfered with the smooth flow of the jet of stock of pulp extruded from the slice of the headbox onto the forming wire.
In the papermaking art, a need has existed for a reliable and accurate apparatus for measuring the jet velocity of pulp extruded from a headbox so that such velocity could be adequately controlled in order to approximate the velocity of the forming wire. By accurately controlling the jet velocity to approximately that of the forming wire, the fibers within the pulp are more evenly distributed over the surface of the forming wire.
In addition to the aforementioned pending patent application, another non-contacting flow velocity device has been developed utilizing the Doppler effect in an ultrasonic flow meter. However, an article published October 1985 in Paper Trade Journal, page 42, and entitled "Advancements in Doppler Flow Metering Improve Accuracy And Reliability" by William T. Smith, states that "The Doppler Flow Meter does have limitations. Heavily scaled or coated pipes, excessive pump noise and vibration, pulsating flows, and some hydrocarbon based applications can pose difficulties for the flow meter. Engineers who require extremely accurate readings in high temperature and/or sonically clean applications will currently not select a Doppler Flow Meter." In view of the extremely noisy environment typical of the forming section of a papermaking machine, it is evident that such Doppler Flow Meters have severe limitations in the foregoing application.
U.S. Pat. No. 4,517,845 to Ransheim et al teaches a flow velocity measuring apparatus for a jet of molten glass. This apparatus corelates amplitude variations in signals using two spaced radiation detectors along the path adjacent the flow path of the glass.
The aforementioned pending patent application, Ser. No. 573,387 is an improvement over the basic concept of U.S. Pat. No. 4,517,845 in the provision of bifurcated fiberoptic bundles. However, a problem has existed in the application of the device of the forementioned pending application in that due to the need for placing the terminations of the fiberoptic bundles approximately 0.6 centimeters from the surface of the jet, particles of the pulp tend to be splashed onto the terminations of the fiberoptic bundles thereby impeding the transmission of the light beams.
The present invention overcomes the aforementioned problem by providing a pressurized curtain of air across the terminations of the fiberoptic bundles thereby inhibiting accumulation of debris that would otherwise impede the transmission of the first and second light beams toward and away from the fluid stream.
Furthermore, in the device disclosed in the copending application, the first and second light beams passing from the terminations of the fiberoptic bundles towards the surface of the stream were generally circular in cross section. Consequently, any slight misalignment of the first and second light beams relative to the direction of flow of the fluid stream resulted in inaccurate signal readings.
The present invention overcomes the problem of inaccuracy of signal readings by providing elongate terminations of the fiberoptic bundles. Such elongate terminations produce elongate beams of light which are transmitted between the terminations of the bundles and the surface of the stream. By providing such elongate beams of light, if the beams of light are slightly misaligned relative to the fluid flow such misalignment causes negligible difference in the signal output.
Therefore, it is a primary objective of the present invention to overcome the aforementioned inadequacies of the prior art devices and to provide a jet velocity measuring apparatus providing a significant contribution to quality control in the papermaking art.
Another object of the present invention is the provision of a jet velocity measuring apparatus which includes a debris-deflecting means disposed adjacent to the first face of a housing for deflecting debris from the first face of the housing thereby inhibiting accumulation of the debris on the first face which would otherwise impede transmission of the first and second beams of light towards and away from the fluid stream.
Another object of the present invention is the provision of a jet velocity measuring apparatus including a first and second plenum defined by the housing for supplying an elongate curtain of debris-deflecting air towards the first and second terminations respectively of the fiberoptic bundles. Such curtain deflects debris away from the housing thereby inhibiting accumulation of debris on the first face of the housing which could otherwise impede transmission of the first and second beams of light towards and away from the fluid stream.
Another object of the present invention is the provision of a jet velocity measuring apparatus including a first and a second fiberoptic bundle, the fiberoptic bundles being elongate in a direction transverse relative to the direction of flow of the fluid stream such that misalignment of the terminations of the first and second fiberoptic bundles relative to the direction of flow of the fluid stream results in substantially no variation between the respective signals generated by the first and second photosensitive devices.
Other objects and advantages resulting from the application of the present invention will be apparent to those skilled in the art.